A biological body generates a wide variety of oscillatory waves having a periodic property in a physiological function and an ecological activity of the biological body, and it is necessary to measure or monitor the number of repetitions per unit time, that is, the vibration frequency for the oscillatory waves more often than not.
For instance, a sports medicine field recommends that a pulse, which is the most basic oscillatory wave that is generated by a biological body, is monitored in a successive manner in order to prevent an accident such as a heart failure and to improve a training effect in the case in which the training is carried out by using the physical exercise support equipment such as an ergometer and a treadmill. Moreover, a lot of people execute a walking to maintain a good health, and a pedometer that is configured to detect an oscillatory wave caused by walking to inform of the number of steps is used at large.
There are a wide variety of oscillatory waves having a periodic property for a biological body. In particular, a pulse that indicates a pulsation of a biological heart is most important and close to one's heart among oscillatory waves having a periodic property. A wide variety of techniques have been proposed for the measuring method of a pulse. The previously existing technology and problems thereof will be described in the following while mainly focusing on a measurement of a pulse.
A measurement of palpation that is carried out by a clinical nurse in a hospital while using a stopwatch is a method that has been adopted through the ages as a measuring method of a pulse. For the measurement of palpation, a pulse wave is sensed by pressing a blood vessel that is close to a thumb on a hand palm side of a wrist with a tip of a finger to sense a generation of a pulse wave for a predetermined time.
However, a certain level of skill is required for the above method, and it is hard to carry out the above method by oneself. Consequently, an apparatus that is configured to electrically measure a pulse wave has been proposed.
A wide variety of apparatuses that are configured to electrically measure a pulse wave have been proposed. In particular, there is widely known a measurement based on a so-called direct counting system in which a pulse wave signal is detected by using a sensor that detects a change of a blood flow in a tip of a finger and the number of pulse wave signals in a minute is counted to be the number of pulses.
However, the direct counting system requires a time period of one minute for a measurement and is not suitable for a continuous measurement of a pulse wave. Consequently, there has been proposed a periodic conversion system in which a time interval of pulse wave signals that have been detected by a sensor, that is, a pulse wave period is calculated, a cumulative value of a pulse wave period that has been obtained by accumulating the pulse wave period by a predetermined number of times is divided by a predetermined number of times to calculate an arithmetic mean value of a pulse wave period, and the arithmetic mean value is converted to pulse waves per minute (see Patent Document 1 for instance).
For the periodic conversion system, a measurement of a pulse wave can be carried out by using a few of pulse wave signals. Moreover, the periodic conversion system is suitable for a continuous measurement of a pulse wave. In the case in which a pulse wave is measured during a physical exercise such as a sport, an error signal of a short period is easily mixed due to a noise caused by a vibration, or a proper pulse wave signal is omitted due to a body motion or the like, whereby an error signal of a long period is generated. As a result, a measured value can vary quite a bit unfortunately.
In order to solve the above problem, there has been proposed a body motion removal system in which a component of a body motion that is contained in a pulse wave signal is removed by using a pulse sensor and a body motion sensor in combination to obtain a pulse wave (see Patent Document 2 for instance).
Moreover, a technique for detecting an electrocardiographic wave has been proposed as another method for preventing a degradation of measurement accuracy due to a body motion noise. For the electrocardiographic wave detection system, since an electrocardiographic wave is stable even in the case in which a body motion is complicated, a measurement during a physical exercise can be carried out. However, a total configuration of an apparatus for the electrocardiographic wave detection system has a tendency to be complicated, and the electrocardiographic wave detection system is not yet widely used as the general technology.
For the previously existing technology that is described in the above Patent Document 2, an improved technique of a composition element that is mainly hardware is disclosed. On the other hand, there also has been proposed a technique for detecting a pulse wave in an accurate fashion by using the signal processing technology that is software (see Patent Document 3 for instance).
For the previously existing technology that is described in the above Patent Document 3, there has been proposed the signal processing technology for improving a degree of accuracy in a measurement of a pulse wave by carrying out a processing for removing a numeric value that cannot be in a range of physiological numeric values in a step for calculating an oscillatory wave from a plurality of pulse wave periods that have been measured.